1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a reflective liquid crystal display device having a tablet.
2. Description of the Related Art
FIGS. 7, 8, and 9 are a cross-sectional view, a principal-part sectional view, and an explanatory view, respectively, of a conventional liquid crystal display device. The conventional liquid crystal display device has a box-shaped casing 21 molded from synthetic resin which is open at the top thereof. The casing 21 is composed of a bottom plate 21a, and four side walls 21b formed on all sides of the bottom plate 21a.
A reflective liquid crystal display element 22 includes a display portion 22a in which liquid crystal is sealed between two transparent glass substrates, and a back reflecting plate 22b disposed outside one of the substrates in the display portion 22a and having a light diffusing ability.
A control member 23 is electrically connected, in which electric parts, such as an IC, are mounted on the side of the liquid crystal display element 22.
A tablet 24 is an input device for converting the coordinates of the position in the plane into electric signals, and comprises a lower substrate 24a made of a transparent glass or the like; a transparent lower electrode portion 24b disposed on the upper surface of the lower substrate 24a and made of indium oxide or the like; a plurality of dot spacers 24c arranged at intervals on the upper surface of the lower electrode portion 24b, which are formed by being printed in a transparent ink of acrylic resin or the like; a film 24d made of a transparent flexible synthetic resin and disposed above the dot spacers 24c; and a transparent upper electrode portion 24e made of indium oxide or the like, which is disposed on the lower surface of the film 24d to oppose the lower electrode portion 24b.
The thickness of the lower substrate 24a is approximately 0.7 mm to 1.8 mm. The dot spacers 24c are formed in a substantially fixed size so that they are 5 .mu.m to 20 .mu.m in height and 50 .mu.m to 100 .mu.m in diameter. The dot spacers 24c are arranged at intervals of 1.5 mm to 2 mm, and serve to space the lower electrode portion 24b and the upper electrode portion 24e. The entire thickness of the tablet 24 is approximately 1 mm to 2 mm.
A light guide 25 is made of a transparent material of acrylic resin or the like, and includes a light guide member 25a having a thickness of approximately 2 mm, and a plurality of semicircular dot patterns 25b formed on one side of the light guide member 25a by being printed in a transparent ink of acrylic resin or the like. These dot patterns 25b are equally sized so that they are approximately 20 .mu.m in height and 50 .mu.m to 100 .mu.m in diameter, and are spaced at equal intervals.
Inside the casing 21, the liquid crystal display element 22, to which the control member 23 is attached, is held with the side of the back reflecting plate 22b down. The light guide 25 is located at a distance of approximately 0.5 mm above the liquid crystal display element 22 with the side of the dot patterns 25b up. The tablet 24 is located at a distance of approximately 0.5 mm above the light guide 25 with the side of the film 24d up. A lamp 26 having a diameter of approximately 1.5 mm and shaped like an elongated rod is placed inside the casing 21 in an appropriate manner so that it is positioned at the end face of the light guide member 25a.
A mounting member 27 formed of a metal plate is composed of a top plate 27a, an opening portion 27b formed in the top plate 27a, and four side plates 27c formed by bending all sides of the top plate 27a. The opening portion 27b is larger than that of an effective display region of the liquid crystal display element 22. The mounting member 27 is fixed the casing 21 in an appropriate manner so that the plate 27a covers the control member 23 and the lamp 26 is held inside the casing 21. Furthermore, the mounting member 27 is mounted so that the effective display region of the liquid crystal display element 22 can be visually recognized from the opening portion 27b via the tablet 24. In this way, the conventional liquid crystal display device is constructed.
In the conventional liquid crystal display device thus constructed, for example, a user presses an input pen (not shown) or the like against the film 24d in the tablet 24 disposed above the liquid crystal display element 22, in response to the contents displayed on the liquid crystal display element 22, so as to deform the film 24d, thereby bringing the upper electrode portion 24e into contact with the lower electrode portion 24b and inputting desired coordinates as electric signals. The display on the liquid crystal display element 22 is appropriately changed according to the input electric signals.
When the conventional liquid crystal display device is used in a dark environment, light from the lamp 26 enters the inside of the light guide member 25a from the end face thereof. In this case, a part of the incident light that travels upward is irregularly reflected by the dot patterns 25b formed on the upper surface of the light guide member 25a to change the angle, and then travels downward, as shown by the arrow X in FIG. 9. Since the light that is incident from the lamp 26 and travels toward the bottom of the light guide member 25a is incident on the lower surface of the light guide member 25a at a small angle, most components thereof are specularly reflected between the lower surface of the light guide member 25a and the atmosphere to travel upward, and are irregularly reflected by the dot patterns 25b to travel downward, as shown by the arrow Y in FIG. 9. Of the light that is thus directed downward, light, which is incident on the lower surface of the light guide member 25a at a nearly perpendicular angle, is transmitted through the light guide member 25a, and is radiated onto the display portion 22a, and the back reflecting plate 22b disposed thereunder in the liquid crystal display element 22. Therefore, the liquid crystal display device can be used in a dark environment. When the conventional liquid crystal display device is used in a light environment, since external light impinges on the back reflecting plate 22b, visibility of the liquid crystal display element 22 can be maintained without using the lamp 26.
In the conventional liquid crystal display device, however, when the lamp 26 is provided, it is necessary to interpose the light guide 25 between the tablet 24 and the liquid crystal display element 22. This increases the thickness and cost of the liquid crystal display device.
Furthermore, it is difficult for the lamp 26 to sufficiently illuminate the entire effective display region of the liquid crystal display element 22. In particular, it is difficult for the light to reach the vicinity of an end face W of the light guide 25 opposite from the side of the lamp 26. Moreover, since some light travels outside from the end face W, as shown by the arrow Z in FIG. 9, it is impossible to sufficiently illuminate the liquid crystal display element 22.